The live-bottom trailers that are of interest herein are used in road construction to haul sand, gravel, rocks, broken pavement and new asphalt. Live-bottom trailers having conveyor belts movable along the floors thereof also include agricultural trailers used for hauling potatoes and other vegetable or grains from a harvester. Known live-floor trailers also include highway transport trailers that are used for transporting dry freight in boxes and on pallets.
Common live-bottom trailers have a conveyor-type rubber belt sliding over the floor of the trailer for moving the content of the trailer toward the rear door of the trailer and for speeding up the unloading of the trailer. The same conveyor belt is also used for more easily loading the trailer. These highway trailers and semi-trailers can carry several tons of material.
Examples of these live-bottom trailers found in the prior art are described in the following documents:    U.S. Pat. No. 3,498,482 issued to M. Lewis on Mar. 3, 1970;    U.S. Pat. No. 3,593,864 issued to W. H. Moser on Jul. 20, 1971;    U.S. Pat. No. 3,704,798 issued to H. L. Carpenture, Jr. et al. on Dec. 5, 1972;    U.S. Pat. No. 3,722,717 issued to L. K. Stryczek on Mar. 27, 1973;    U.S. Pat. No. 3,888,366 issued to E. D. Prahst on Jun. 10, 1975;    U.S. Pat. No. 3,953,170 issued to J. O. Webb on Apr. 27, 1976;    U.S. Pat. No. 3,998,343 issued to V. E. Fors on Dec. 21, 1976;    U.S. Pat. No. 4,162,735 issued to M. Lewis on Jul. 31, 1979;    U.S. Pat. No. 4,431,360 issued to M. Maeno in Feb. 14, 1984;    U.S. Pat. No. 4,518,303 issued to W. H. Moser on May 21, 1985;    U.S. Pat. No. 4,664,583 issued to J. N. Gust on May 12, 1987;    U.S. Pat. No. 4,747,747 issued to S. M. Fusco et al. on May 31, 1988;    U.S. Pat. No. 4,842,471 issued to G. L. Hodgetts on Jun. 27, 1989;    U.S. Pat. No. 6,837,668 issued to D. J. B. Brown on Jan. 4, 2005;    U.S. Pat. No. 7,147,423 issued to R. Golden et al. on Dec. 12, 2006.
In another type of live-bottom trailers, the load inside the trailer is moved on steel cables that are laid along the floor of the trailer. In these applications, a conveyor belt is not used. The cables are pulled along the floor of the trailers by winches or hydraulic cylinders, for carrying the load over the floor surface. Because the total surface of the cables that is in contact with the floor of the trailer is smaller than the footprint of the load to be moved, and because there is a lesser coefficient of friction provided by the cables, the force required to overcome friction is considerably reduced.
Examples of trailers in the prior art, having parallel cables laid on the floor thereof are listed below:    U.S. Pat. No. 3,272,358 issued to F. Thompson on Sep. 13, 1966;    U.S. Pat. No. 4,082,196 issued to D. W. Lutz et al. on Apr. 4, 1978;    U.S. Pat. No. 4,111,318 issued to D. E. Lutz on Sep. 5, 1978;    U.S. Pat. No. 4,113,122 issued to D. E. Lutz on Sep. 12, 1978;    WO 87/01996 filed by Luigi Pellegrino, published on Apr. 9, 1987;    U.S. Pat. No. 5,171,122 issued to L. Pellegrino on Dec. 15, 1992.
A number of prior art documents also disclose movable bulkhead arrangements for pushing the content of a trailer all at once toward the rear door of the trailer. These documents are listed herein below for illustrating progress made in the art:    U.S. Pat. No. 2,606,677 issued to A. E. Snedeger on Aug. 12, 1952;    CA Patent 1,031,735 issued to H. D. Rezac on May 23, 1978;    U.S. Pat. No. 5,143,508 issued to D. E. Lutz et al. on Sep. 1, 1992;    U.S. Pat. No. 5,314,290 issued to D. E. Lutz et al. on May 24, 1994.
The various concepts described in the prior art have a common advantage of emptying a trailer in a more efficient manner. Although the advantages of a conveyor belt; a series of parallel cables moving on the bottom surface of a trailer, and a movable bulkhead are easy to appreciate, a combination of the three elements wherein the cables are used to move both the conveyor belt and the bulkhead, has not been seen in the prior art. This deficiency in the art may be explained by the challenges that this combination represents to designers and builders of these trailers.
One of the challenges encountered in the design and construction of a live-bottom trailer with floor cables mounted under a conveyor belt is a relative movement between the conveyor belt and the floor cables. This relative movement could causes the gouging of grooves in the bottom surface of the belt and can destroy the belt in a relatively short time.
Another challenge is a total weight of the combination. Truck owners are oftentimes paid by the ton of material transported. The weight of accessories mounted inside a trailer takes away available space and available cargo weight for that trailer. Therefore the advantages of a live-floor mechanism must have sufficient value to offset the losses in revenue from a reduction of cargo weight for that trailer.
It is believed that this weight restriction factor, primarily, has been a major impediment in the past for designing and building a live-bottom trailer having a conveyor belt; parallel cables mounted under the belt and a bulkhead that is movable with the belt and cables.